Sperm whale description

The sperm whale (Physeter macrocephalus) is the largest of the toothed whales, with males growing up to 20 metres in length. The sperm whale also has the largest brain of any living animal, and it was a sperm whale that was pitted against Captain Ahab in Herman Melville’s classic novel, Moby Dick (2).

Sperm whales have huge square heads, comprising almost a third of the total body length (2)(3); indeed the specific name macrocephalus means large head. Uniquely among cetaceans, the single blowhole is located on the left of the head rather than on the top (3) and so these whales are easily identified at a distance by their low, bushy spout, which is projected forward and slightly to the left (2). Further down the body toward the tail there is usually a large hump on the back, followed by a series of smaller bumps (3). The dark brown to bluish-black skin, which is splotched and scratched, is said to have a texture like that of a plum stone (2)(3). Males tend to be somewhat larger and heavier than females (3), and have larger heads in relation to their body size (6).

The huge heads of sperm whales contain a large cavity, the spermaceti organ, filled with a waxy liquid called spermaceti oil. This wax can be cooled or heated, possibly by water sucked in through the blowhole, and thus shrinks and increases in density (helping the whale sink), or expands and decreases in density (helping the whale rise to the surface) (5). Whalers likened the substance to semen, and this is the origin of the common name of the species (6).

Related species

Sperm whale biology

The sperm whale lives in either nursery or bachelor groups. Nursery groups consist of a number of adult females and immature males and females (2)(6). Males leave these groups when they become mature and join bachelor groups, which consist of males of 7 to 27 years of age (6). Older males live in small groups or singly, and visit nursery groups to mate with females during the breeding season (6). Most groups of sperm whales tend to number between 10 and 15 individuals (4).

This magnificent ocean mammal uses echolocation to find its prey in the dark ocean depths (6). When foraging, powerful sound waves are emitted from the large head; these can stun and even kill the squid, octopuses and fish on which it feeds (4). The sperm whale can make deep dives to depths of up to 3,000 metres (almost 2 miles) that can last as long as two hours (2)(6). This is the deepest dive made by any species of mammal (6).

Male sperm whales reach maturity at 10 years of age, but they do not begin to mate until they are around 19 years old and a length of 13 metres. Females become mature at between 7 and 11 years, when they are around 9 metres in length. A single calf is born between July and November after a gestation period of around 16 months. The calf is suckled for up to two years (4). Groups of females protect their young by adopting a defensive ‘marguerite formation’ in which the calves are placed in the centre of the group surrounded by a circle of females, facing tail outwards (4).

Species with a similar range

Sperm whale habitat

Although primarily an inhabitant of the open ocean in offshore areas, the sperm whale may also occasionally be seen closer to land, providing that the water is deeper than 200 metres (2). It occurs in tropical to sub-polar waters (2).

Sperm whale status

Sperm whale threats

The sperm whale has a long history of commercial exploitation (1). Large-scale hunting began in 1712 in the North Atlantic, based at Nantucket in America (4). It was not widely hunted for its meat, but for ambergris and spermaceti. Ambergris is a substance that collects around the indigestible beaks of squid in the stomach of the whale, and was highly prized for use as a fixative in the perfume industry. Although artificial alternatives are now available, some perfume makers prefer to use ambergris today. Spermatceti was used in the production of cosmetics and candles (7). The sperm whale still has an economic value today for meat in Japan. Since the 1980s, the International Whaling Commission brought an international moratorium on whaling into force. Despite this measure, Japan continues to hunt sperm whales, and relatively small numbers are taken each year with hand harpoons at Lamalera, Indonesia (1). Further threats include entanglement in fishing gear and collisions with boats (1). Although whaling has, with the exceptions outlined above, largely ceased, the after-effects of such prolonged and intensive hunting are still being felt today. It is thought that the selective hunting of the largest, breeding males will have decreased pregnancy rates, and the loss of the largest females from nursery groups would have decreased the survival of the groups (1).

Sperm whale conservation

As a species, the sperm whale is not facing immediate threat, but some populations need to be carefully monitored, and there is need for tight management of any exploitation (1). In the eastern tropical Pacific, recent whaling was extremely intensive, and birth rates at present are very low. The Mediterranean population is particularly susceptible to collisions with ships and entanglement with fishing gear (1).

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